diff --git a/composer.json b/composer.json
index 1d67cac162..8b733b2c2d 100644
--- a/composer.json
+++ b/composer.json
@@ -24,7 +24,7 @@
         "josegonzalez/dotenv": "~4.0.0",
         "league/oauth2-server": "^8.5",
         "logiscape/mcp-sdk-php": "^2.0",
-        "mobiledetect/mobiledetectlib": "~3.74.4",
+        "mobiledetect/mobiledetectlib": "~4.8.03",
         "nikic/php-parser": "~5.8.0",
         "nyholm/psr7": "^1.8",
         "psr/http-message": "~1.1",
diff --git a/composer.lock b/composer.lock
index f5de3ac9e6..fdd3e5fb40 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "863cc00b16dc953173b7209c798a7293",
+    "content-hash": "bb6d8be00e7ad6419391c99d0264dff8",
     "packages": [
         {
             "name": "cakephp/authentication",
@@ -2498,34 +2498,34 @@
         },
         {
             "name": "mobiledetect/mobiledetectlib",
-            "version": "3.74.4",
+            "version": "4.8.10",
             "source": {
                 "type": "git",
                 "url": "https://github.com/serbanghita/Mobile-Detect.git",
-                "reference": "e72098eba91e5f16278b17d42ca193ae71e4ae0a"
+                "reference": "96b1e1fa9a968de7660a031106ab529f659d0192"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/serbanghita/Mobile-Detect/zipball/e72098eba91e5f16278b17d42ca193ae71e4ae0a",
-                "reference": "e72098eba91e5f16278b17d42ca193ae71e4ae0a",
+                "url": "https://api.github.com/repos/serbanghita/Mobile-Detect/zipball/96b1e1fa9a968de7660a031106ab529f659d0192",
+                "reference": "96b1e1fa9a968de7660a031106ab529f659d0192",
                 "shasum": ""
             },
             "require": {
-                "php": ">=7.4"
+                "php": ">=8.0",
+                "psr/simple-cache": "^3"
             },
             "require-dev": {
-                "friendsofphp/php-cs-fixer": "^3.14",
-                "phpunit/phpunit": "^9.6",
-                "squizlabs/php_codesniffer": "^3.7"
+                "friendsofphp/php-cs-fixer": "^v3.75.0",
+                "phpbench/phpbench": "^1.2",
+                "phpstan/phpstan": "^2.1.11",
+                "phpunit/phpunit": "^9.6.22",
+                "squizlabs/php_codesniffer": "^3.12.1"
             },
             "type": "library",
             "autoload": {
                 "psr-4": {
                     "Detection\\": "src/"
-                },
-                "classmap": [
-                    "src/MobileDetect.php"
-                ]
+                }
             },
             "notification-url": "https://packagist.org/downloads/",
             "license": [
@@ -2535,7 +2535,7 @@
                 {
                     "name": "Serban Ghita",
                     "email": "serbanghita@gmail.com",
-                    "homepage": "https://mobiledetect.net",
+                    "homepage": "http://mobiledetect.net",
                     "role": "Developer"
                 }
             ],
@@ -2550,7 +2550,7 @@
             ],
             "support": {
                 "issues": "https://github.com/serbanghita/Mobile-Detect/issues",
-                "source": "https://github.com/serbanghita/Mobile-Detect/tree/3.74.4"
+                "source": "https://github.com/serbanghita/Mobile-Detect/tree/4.8.10"
             },
             "funding": [
                 {
@@ -2558,7 +2558,7 @@
                     "type": "github"
                 }
             ],
-            "time": "2026-04-15T08:43:14+00:00"
+            "time": "2026-01-09T16:21:59+00:00"
         },
         {
             "name": "nikic/php-parser",
diff --git a/plugins/baser-core/composer.json b/plugins/baser-core/composer.json
index e90a43703a..229f3fe698 100644
--- a/plugins/baser-core/composer.json
+++ b/plugins/baser-core/composer.json
@@ -15,7 +15,7 @@
         "firebase/php-jwt": "~7.0.2",
         "ezyang/htmlpurifier": "~4.19.0",
         "robmorgan/phinx": "0.16.10",
-        "mobiledetect/mobiledetectlib": "~3.74.4",
+        "mobiledetect/mobiledetectlib": "~4.8.03",
         "nikic/php-parser": "~5.8.0",
         "cakephp/debug_kit": "~5.2.4",
         "ext-json": "*",
diff --git a/plugins/baser-core/tests/TestCase/Utility/BcComposerTest.php b/plugins/baser-core/tests/TestCase/Utility/BcComposerTest.php
index eea0c01669..ec6df13f09 100644
--- a/plugins/baser-core/tests/TestCase/Utility/BcComposerTest.php
+++ b/plugins/baser-core/tests/TestCase/Utility/BcComposerTest.php
@@ -135,6 +135,8 @@ public function test_require()
         $data = str_replace('"cakephp/migrations": "~4.9.7"', '"cakephp/migrations": "^4.0.0"', $data);
         // CakePHP5.0.10 と共存できる cakephp/bake（3.0.1〜3.1.1）は nikic/php-parser 4系を要求するため緩和する
         $data = str_replace('"nikic/php-parser": "~5.8.0"', '"nikic/php-parser": "^4.13.2 || ^5.0"', $data);
+        // baserCMS5.1系は mobiledetect/mobiledetectlib 3系を要求するため緩和する
+        $data = str_replace('"mobiledetect/mobiledetectlib": "~4.8.03"', '"mobiledetect/mobiledetectlib": "^3.74 || ^4.8"', $data);
         $data = preg_replace($regex, '', $data);
         $file->write($data);
         BcComposer::setup('php');
@@ -205,6 +207,8 @@ public function testUpdate()
         $data = str_replace('"cakephp/migrations": "~4.9.7"', '"cakephp/migrations": "^4.0.0"', $data);
         // CakePHP5.0.10 と共存できる cakephp/bake（3.0.1〜3.1.1）は nikic/php-parser 4系を要求するため緩和する
         $data = str_replace('"nikic/php-parser": "~5.8.0"', '"nikic/php-parser": "^4.13.2 || ^5.0"', $data);
+        // baserCMS5.1系は mobiledetect/mobiledetectlib 3系を要求するため緩和する
+        $data = str_replace('"mobiledetect/mobiledetectlib": "~4.8.03"', '"mobiledetect/mobiledetectlib": "^3.74 || ^4.8"', $data);
         $data = preg_replace($regex, '', $data);
         $file->write($data);
         BcComposer::setup('php');